Hibernate主键ID自动生成两种方法示例
Hibernate主键ID自动生成两种方法示例，用uuid生成唯一的主键， 用这种方法，如果对象的id为null，保存时会自动生成一个UUID，如
版本：hibernate-3.2.7
方法之一： 用uuid生成唯一的主键， 用这种方法，如果对象的id为null，保存时会自动生成一个UUID，如果id不为null，保存时会从数据库中找出这条记录，然后执行update,如果未找到是抛出异常。
Xxxclass.hbm.xml代码
Xxxclass.java代码
方法之二： 用org.hibernate.id.UUIDHexGenerator生成唯一的主键， 用这种方法，如果对象的id为null，，保存时会自动生成一个UUID，如果id不为null，保存时会从数据库中找出这条记录，然后执行update,如果未找则执行insert。
Xxxclass.hbm.xml代码
Xxxclass.java代码
Assignedidmodel.java代码
Assigncopiedid.java代码
总结： 两种方法相比之下，方法一比较简单，能满足一般情况，项目中用的比较多。方法一无法处理时才用方法二，例如从其它系统数据库复制表的记录时用。
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